Publication Date

2019-05-01

Availability

Open access

Embargo Period

2019-05-01

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology and Ecology (Marine)

Date of Defense

2019-04-05

First Committee Member

Andrew Baker

Second Committee Member

Diego Lirman

Third Committee Member

Maria Estevanez

Abstract

Coral reef ecosystems are experiencing rising sea surface temperatures globally and nutrient pollution is also widespread. Kāne’ohe Bay on O’ahu, Hawai’i has experienced altered nutrient regimes in the past few decades as well as bleaching events as a result of temperature anomalies. Elevated nutrient concentrations can exacerbate heat stress and make corals more susceptible to bleaching by increasing symbiont densities. To examine the effects of heat stress and elevated nutrients, Pocillopora acuta larvae from Kāne’ohe Bay were exposed to elevated temperatures (28-31°C) and elevated nutrient concentrations (5-uM NO3 and 1-uM PO4) over a 5-day period and were assessed for survivorship, settlement, respiration, size, and symbiont cell densities. P. acuta maintained high survivorship (91-98%) over the course of the study, but elevated nitrate significantly reduced survivorship. High temperature, nutrients, and interactions all increased settlement rates, decreasing time to competency. Faster settlement rates can increase local retention and decrease connectivity between reefs. While a temperature of 29°C caused a decrease in respiration rate, there were no apparent effects of temperature or nutrients on larval size or symbiont density despite. Nutrient analyses revealed increased uptake of phosphate in nitrate + phosphate treatments, suggesting that elevated phosphate concentrations restore the N:P ratio necessary to maintain functional symbioses between P. acuta and their symbionts, allowing them to maintain symbiont densities and high survivorship. The ability of P. acuta larvae to maintain their mutualistic symbiosis while exposed to multiple stressors suggests that they have mechanisms for coping with heat and elevated nutrients.

Keywords

coral; larvae; coral reproduction; climate change; eutrophication; coral bleaching

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